Connecting a DVR to computer monitor

Hello,

I am having trouble connecting a DVR to a computer monitor and wondering if anyone can help.

It's old equipment i'm putting in a spare room. I am connecting a Strong SRT 5425 set-top box to Benq FP202 monitor. (HDMI output of the box to DVI monitor input with HDMI-DVI cable)

The monitor works fine connected to my laptop with the HDMI-DVI cable (so the cable works). The set-top box works fine connected to HDMI-HDMI on another TV (so HDMI out works). But the monitor and box don't work together. I have tried changing the box settings (576p, 720p). What am I doing wrong?

Many thanks,

David